[PATCH 1/2][PR GDB/32956] gdb: implement linux namespace support for fileio_stat

[Fabian Kilger <kilger@sec.in.tum.de>]

The new algorithm to look for a build-id-based debug file
(introduced by commit 22836ca88591ac7efacf06d5b6db191763fd8aba)
makes use of fileio_stat. As fileio_stat was not supported by
linux-namespace.c, all stat calls would be performed on the host
and not inside the namespace

---
 gdb/linux-nat.c            | 14 ++++++++
 gdb/linux-nat.h            |  3 ++
 gdb/nat/linux-namespaces.c | 71 ++++++++++++++++++++++++++++++++++++++
 gdb/nat/linux-namespaces.h |  6 ++++
 4 files changed, 94 insertions(+)

diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 3f252370c7b..478a7977c4d 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -4585,6 +4585,20 @@ linux_nat_target::fileio_open (struct inferior *inf, const char *filename,
   return fd;
 }
 
+/* Implementation of to_fileio_stat.  */
+int
+linux_nat_target::fileio_stat (struct inferior *inf, const char *filename,
+			       struct stat *sb, fileio_error *target_errno)
+{
+  int r = linux_mntns_stat (linux_nat_fileio_pid_of (inf),
+			    filename, sb);
+
+  if (r == -1)
+    *target_errno = host_to_fileio_error (errno);
+
+  return r;
+}
+
 /* Implementation of to_fileio_readlink.  */
 
 std::optional<std::string>
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index b630b858e34..42d1ec142b3 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -108,6 +108,9 @@ class linux_nat_target : public inf_ptrace_target
 		     const char *filename,
 		     fileio_error *target_errno) override;
 
+  int fileio_stat (struct inferior *inf, const char *filename,
+		   struct stat *sb, fileio_error *target_errno) override;
+
   int fileio_unlink (struct inferior *inf,
 		     const char *filename,
 		     fileio_error *target_errno) override;
diff --git a/gdb/nat/linux-namespaces.c b/gdb/nat/linux-namespaces.c
index 19a05eec905..aa74e9df950 100644
--- a/gdb/nat/linux-namespaces.c
+++ b/gdb/nat/linux-namespaces.c
@@ -233,6 +233,12 @@ enum mnsh_msg_type
        MNSH_RET_INT.  */
     MNSH_REQ_SETNS,
 
+    /* A request that the helper call stat.  The single
+       argument (the filename) should be passed in BUF, and
+       should include a terminating NUL character.  The helper
+       should respond with a MNSH_RET_INTSTR.  */
+    MNSH_REQ_STAT,
+
     /* A request that the helper call open.  Arguments should
        be passed in BUF, INT1 and INT2.  The filename (in BUF)
        should include a terminating NUL character.  The helper
@@ -283,6 +289,10 @@ mnsh_debug_print_message (enum mnsh_msg_type type,
       debug_printf ("ERROR");
       break;
 
+    case MNSH_REQ_STAT:
+      debug_printf ("STAT");
+      break;
+
     case MNSH_REQ_SETNS:
       debug_printf ("SETNS");
       break;
@@ -514,6 +524,20 @@ mnsh_handle_setns (int sock, int fd, int nstype)
   return mnsh_return_int (sock, result, errno);
 }
 
+
+/* Handle a MNSH_REQ_STAT message.  Must be async-signal-safe.  */
+
+static ssize_t
+mnsh_handle_stat(int sock, const char *filename)
+{
+  struct stat sb;
+  int stat_ok = stat(filename, &sb);
+
+  return mnsh_return_intstr(sock, stat_ok, &sb,
+			    stat_ok == -1 ? 0 : sizeof (sb),
+			    errno);
+}
+
 /* Handle a MNSH_REQ_OPEN message.  Must be async-signal-safe.  */
 
 static ssize_t
@@ -574,6 +598,11 @@ mnsh_main (int sock)
 		response = mnsh_handle_setns (sock, fd, int1);
 	      break;
 
+	    case MNSH_REQ_STAT:
+	      if (size > 0 && buf[size - 1] == '\0')
+		response = mnsh_handle_stat(sock, buf);
+	      break;
+
 	    case MNSH_REQ_OPEN:
 	      if (size > 0 && buf[size - 1] == '\0')
 		response = mnsh_handle_open (sock, buf, int1, int2);
@@ -765,6 +794,10 @@ mnsh_maybe_mourn_peer (void)
   mnsh_send_message (helper->sock, MNSH_REQ_OPEN, -1, flags, mode, \
 		     filename, strlen (filename) + 1)
 
+#define mnsh_send_stat(helper, filename) \
+  mnsh_send_message (helper->sock, MNSH_REQ_STAT, -1, 0, 0, \
+		     filename, strlen (filename) + 1)
+
 #define mnsh_send_unlink(helper, filename) \
   mnsh_send_message (helper->sock, MNSH_REQ_UNLINK, -1, 0, 0, \
 		     filename, strlen (filename) + 1)
@@ -945,6 +978,44 @@ linux_mntns_access_fs (pid_t pid)
   return MNSH_FS_HELPER;
 }
 
+
+/* See nat/linux-namespaces.h.  */
+int
+linux_mntns_stat (pid_t pid, const char *filename,
+		  struct stat *sb)
+{
+  enum mnsh_fs_code access = linux_mntns_access_fs (pid);
+  struct linux_mnsh *helper;
+  int stat_ok, error;
+  ssize_t size;
+
+  if (access == MNSH_FS_ERROR)
+    return -1;
+
+  if (access == MNSH_FS_DIRECT)
+    return stat(filename, sb);
+
+  gdb_assert (access == MNSH_FS_HELPER);
+
+  helper = linux_mntns_get_helper ();
+
+  size = mnsh_send_stat (helper, filename);
+  if (size < 0)
+    return -1;
+
+  size = mnsh_recv_intstr (helper, &stat_ok, &error, sb, sizeof (*sb));
+
+  if (size < 0)
+    {
+      stat_ok = -1;
+      errno = error;
+    }
+  else
+    gdb_assert (stat_ok == -1 || size == sizeof (*sb));
+
+  return stat_ok;
+}
+
 /* See nat/linux-namespaces.h.  */
 
 int
diff --git a/gdb/nat/linux-namespaces.h b/gdb/nat/linux-namespaces.h
index 4327292950b..825cb27eb2d 100644
--- a/gdb/nat/linux-namespaces.h
+++ b/gdb/nat/linux-namespaces.h
@@ -58,6 +58,12 @@ enum linux_ns_type
 
 extern int linux_ns_same (pid_t pid, enum linux_ns_type type);
 
+/* Like stat(2), but in the mount namespace of process
+   PID.  */
+
+extern int linux_mntns_stat (pid_t pid, const char *filename,
+			     struct stat *sb);
+
 /* Like gdb_open_cloexec, but in the mount namespace of process
    PID.  */
 
-- 
2.49.0